Ruthenium is a metal having superior thermal and chemical stability. Owing to high work function, easy etching and easier thin film formation as compared to other metals such as Pt, Ir, etc., it is promising as an electrode material of a next-generation memory device. Also, ruthenium has good conductivity with a specific resistance of 7.1-7.6 μΩ·cm and ruthenium oxide is capable of improving leakage current characteristics because of low specific resistance of about 40 μΩ·cm and high work function of 4.7-4.9 eV.
As precursors for the preparation of ruthenium metal or ruthenium oxide thin films, (η6-arene)(η4-diene)Ru [Giovanni Vitulli et al., Inorganics Chimica Acta, vol. 149, 1988, 235-239]; (toluene)Ru(COD), (toluene)Ru(norbonadiene), etc. [International Patent Application Publication No. WO 2008/044478]; (1,3-cyclohexadienyl)(4-isopropyl-1-methylbenzene)Ru, etc. as (diene)(Rbenzene)ruthenium, or the like are known. Although these precursors are liquid at room temperature and have vapor pressure favorable for formation of ruthenium thin films, the process window is narrow during thin film formation under continuous heating. In particular, since step coverage is poor when depositing ruthenium or ruthenium oxide thin film on a substrate having a trench structure with a specific aspect ratio, they are inapplicable to large-scale production.
Korean Patent Application Publication No. 2010-60482 discloses a ruthenium precursor compound having high thermal stability and high vapor pressure whose properties are not degraded even under continuous heating. Korean Patent Publication No. 2010-60482 discloses a ruthenium compound having a cyclic alkene group of 3-8 carbon atoms having 1-4 double bond(s) as a ligand (L) and describes (1,5-cyclooctadienyl)(ethylbenzene)ruthenium represented by Chemical Formula A as a specific example of the compound.

Korean Patent Application Publication No. 2010-60482 describes that the ruthenium compound represented by Chemical Formula A is solid at room temperature with a melting point of 24-25° C. and the precursor exhibits superior thermal stability and vaporizing property, with T1/2 of 247° C. in thermogravimetric analysis (TGA) and showing constant weight loss without decomposition in the temperature range of 80-150° C. However, according to Korean Patent Publication No. 2010-60482, the precursor having the ligand introduced vaporizes quickly with few residues on a substrate in the deposition temperature range of 130-160° C. and preparation of high-purity thin film has not been demonstrated.
The inventors of the present invention have prepared a ruthenium precursor compound having a specific ligand introduced, which shows T1/2 of 230° C. in thermogravimetric analysis (TGA), less than 1.5% of residue rate and superior thermal stability with constant weight loss without decomposition of the precursor in the temperature range of 80-120° C. and fast vaporization and few residues of the precursor in the temperature range of 130-160° C. In particular, the precursor compound exhibits superior step coverage when forming a ruthenium thin film through atomic layer deposition (ALD).